Geology of Siberia: Encyclopedia Arctica Volume 1: Geology and Allied Subjects

CONTENTS

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Contents -#2

GEOLOGY OF SIBERIA

Geological studies of Siberia were less thorough than the investigation of the Russian Platform, the Urals, and the Caucasus prior to the October Revolution. A band of some width, along the ^ [^ Trans-Siberian - M. E. B. ^ ]^ Railway trunk line, was known best; during the period in which the Railway was built (between 1892 and 1910) several reconnaissance parties, working from the Urals to Vladivostok, produced a series of maps drawn to scales of from twenty to forty versts per decimeter. The Altai Mountain region, an imperial preserve, was studied in rather more detail, but government geologists were able to produce ten-verst-per ^ -^ decimeter maps only for the Kuznetsk Basin, the Salair, the western slope of the Kuznetsk Alatau, and the northern margin of the Altai before the First World War broke out. Between 1899 and 1913 other geological parties studied the Y ^ e^ nisei, Lena, Barguzin, and Amur-Maritime gold areas, and the Minusinak Depression, mapping these areas on a scale of one or two versts per decimeter.

In 1912 the Geological Survey began to recruit geologists for local studies, chiefly of the southern belt, in regions possessing features of special interest, and also in the Viliui and Aldan river basins, Sakhalin, and the Okhotsk and Anadyr regions. These field parties filled in the outline of geological data gathered by the Academy of Science of Geographical Society field parties

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over the vast extent of northern Siberia during a number of years; but their reports were essentially rather sketchy reconnaissance reports — vast areas within the regions studied were not examined. Privately sponsored field parties in the arctic Urals, the Chukotsk Peninsula, and Kamchatka gathered small amounts of data on these regions at the turn of the century. Thus, only the southern portions of Siberia had been investigated by geologists prior to 1917, and even such reconnaissance had not touched the Golodnsia Steppe of Kazakhstan, the Altai Mountains, and the Western and Eastern Saian, and these regions remained virtually unexplored. The great northern half of the country had been crossed only by occasional reconnaissance parties, and information about the geology of the area was fragmentary and questionable.

It is worthy of note that only two government geologists were maintained in all of Siberia before the Revolution; one was attached to the Irkutsk Mines Administration in 1888, and the other to the Tomsk Mines Administration in 1905. Directives drawn up in 1892 indicate that both used St. Petersburg as their base of operations.

A rapid expansion of Siberian geological studies took place after the Revolution, and as early as 1919, government geologists who were working in Siberia were unable to return to St. Petersburg across the Civil War front. They established permanent headquarters at Tomsk and organized for continuous research. This developed into the Siberian Geological Survey, which later became the Siberian Department of the Soviet Geological Survey, and, after a lapse of several years, was combined with the research organization that had its headquarters at Irkutsk into the Western Siberian Department of the Survey. Geological activity, centered at Vladivostok, underwent a similar development. When the Survey subsequently became the Central Geological

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Research and Development Institute, these Departments became first Trusts, and later Geological Administration ^ s^ ; such Administrations were established at Semipalatinak and I ^ Y^ akutsk, and the Khaberovsk Geological Administration replaced the Far Eastern.

Geologists were attached to a number of organizations in the coal, petroleum, and ferrous and nonferrous metals field ^ s^ , and undertook special tasks there.

The Academy of the Sciences of the U.S.S.R., which led in the study of the geology of Siberia before the Revolution, continued to send out field parties for regional stratigraphic, petrographic, geochemical, tectonic, and geomorphologic studies. The growth of geological research sponsored by the various geological Administrations and People’s Commissariats was such, however, that the relative scope of Academy efforts was dwarfed even though substantial contributions to the study of a number of problems and regions still came from this source. The efforts of the Russian Geographical Society in this sphere became insignificant, and research sponsored by private individuals and concerns disappeared altogether.

The search for mineral deposits of economic importance held top priority during the Soviet regime’s first decade; this was due to the urgency of in– dustrial development. The programming of prospecting for Siberia lagged far behind. Steps were taken to remedy this situation, and a geological map (1:1,000,000) of the southern portion of Siberia appeared toward the end of the decade. Maps drawn to larger scales for various regions appeared, and maps of assorted merit, drawn to a variety of scales, appeared for the Kuznetsk Basin, the Altai, portions of Kazakhstan, the Minusinek Depression, the Kuznetsk Al ^ a^ tau, the Western and Eastern Saian, the Cis-Baikel ^ Cisbaikal^ , the Lena region, and Kamchatka.

The Geological Map of the Soviet Union (1:2,500,000), published in 1939, still contained blank spots, but these are growing smaller.

We now turn to the progress of regional geological and tectonic studies.

The West Siberian Lowland occupies the northern half of the area between the Ural Mountains and the Y ^ e^ nisei River, and possesses a southward extension — the Turgai Depression — that lies between the Urals and the Kazakh Steppe. The fragmentary nature of earlier studies in the area was due to sparse population and the absence of deposits of the more valuable minerals. The Soviet period, however, saw considerable progress in the investigation of the area. Oil possibilities, water supply, potential railway routes, brine lakes, and peat deposits were studied, as well as moraines and signs of glaciations in the north, and coal deposits in the Turgai Depression; several geologists were occupied with those tasks.

The region’s river valleys were investigated, the suspected eastward extension of the folding and igneous intrusion of Paleozoic strata in the Urals were established, while well records and geophysical investigations along railroad routes revealed that the folded Paleozoic underlies slightly deformed Quaternary, Tertiary, Cretaceous, and Jurassic formations. Escaping gas and evidence of petroleum have been found at some points.

Several field parties also studied the salt, sod s ^ a^ , and mineral lakes of the Kulundim and Barsbin steppes; these investigations brought to light a great deal of information concerning the processes and conditions of salt deposition and point to the possible future utilization and development by chemical industries.

A varied fauna, a not inconsiderable flora, and a large amount of informa– tion about the Quaternary, Tertiary, local Cretaceous, Jurassic, and Devonian ^periods^

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were gathered in studies of the deep-out valleys of the Irtysh, the Ob, and their tributaries.

Several preglacial, glacial, and interglacial stages have been identified in the regional Quaternary sequence. The Tertiary sequence contains terri– genous formations of Miocene and Pliocene age, and occasional Paleocene, Eocene, or Oligocene marine rocks; Cretaceous, Jurassic, Carboniferous, and Upper Devonian formations, however, crop out only in the Ob Valley above Novosibirsk. The rich and varied fauna found in the Pliocene rocks near Pavlodar was described by Orlov.

A number of investigators penetrated the forested and unforested tundra west of the Ob and along the western tributaries of the Y ^ e^ nisei by following the Taz River. They have studied the glacial and interglacial stages, and the Arctic Marine Transgression of the Gydan ^ ski^ and Iamal peninsulas. For example, by mapping the distribution of erratics, Gromov was able to fix the boundary between the ice sheet moving down from the Urals and the sheet moving from the highlands beyond the Yenisei River. The southern boundaries of the component stages of two glaciations (the Riss, the W u ^ ü^ rm, and possibly of an earlier one) are still in doubt, as are the locations of the outlets of ancient lakes that came into being when moraines damned the Ob and Irtysh. Gromov found an oil-bearing formation of upper Volga age in the area. Studies were made of the peat deposits and soils of the tundras and well as their hydrology and geomorphology. Edelshtein integrated the hydrological date.

The Quaternary and upper Tertiary strata in the Turgai Depression were mapped (Paleocene formations frequently outcrop beneath the latter). The abundant fauna of the Turgai Paleocene was known in pre-Revolutionary times from studies at Lake Chelkar and along the Dzhilanchik River.

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A. Borisiak of the Academy began to catalogue this fauna at that time, and he continued the task after the Revolution. Cretaceous and coal-bearing Jurassic formations crop out locally along the eastern and western borders of the Depression. The soils and ground water of the Ciz-Aral have been investigated. Bykov and Baiarunas have described the geology of the area, and Prigorovski described the coal deposits.

Tectonic investigations in the area have revealed that the Mesozoic and Cenozoic formations that cover the more intensely deformed Pale ^ o^ zoic for great distances eastward are only locally deformed, and this in the vicinity of the Irtysh and Ob rivers, where extremely broad folds are present. This folding becomes somewhat more pronounced toward the Urals piedmont, and is particularly noticeable in the Rhaetic-Liassic coal measures of the Cheliabinsk Basin, and in the Cretaceous and Jurassic formations north and south of the Basin, where relatively recent fault movements have brought up Jurassic, Cretaceous, and Tertiary formations through varying amplitudes.

Northern Kazakhstan (Altai Mountains and mining district omitted). The geological investigation of this region made great progress after the Revolution because important mining projects were initiated here, and also because flat relief and the absence of a forest cover make exploration simple. The region, consequently, is probably the most thoroughly investigated in all Siberia, in spite of the fact that the structure is extremely complex. The stratigraphic column carries representatives of every period from the Archean to the Quaternary, inclusive, and igneous bodies are abundant. The regional pre-Cambrian is repre– sented by the Archean (gneisses and mica schists) and the Proterozoic (quartzites, phyllites, sericitic and gra m phitic schists, marbles, and porphyrites); each section is divided into two unconformable divisions.

Middle and Upper Cambrian formations that carry trilobite, archaeocynthid, and brachiopod fauna, and fossil algae make their appearance in limestones and shales at various localities.

The Ordovician and Silurian sequences are even more complete. They are represented by beds runging from Osarkian to Downt ow nian age, and carry grap– tolite, pteropod, brachiopod, coral, and other invertebrate remains; limestones and shales dominate the lithology.

Extrusive products of submarine volcanism are found together with the sedimentary Cambrian, Ordovician, and Silurian rocks; thus, fully half the Cambrian sequence in the Chingiz Range consists of lava analogues which are also found in central Kazakhstan. The Ordovician also contains tuffs and volcanic breccias in the latter area, but it is the upper Silurian that contains the effusives in the Chingiz and Karaganda areas. The volume of effusives in Tarbagatai and the Ciz-Balkhash is somewhat less.

Recent studies have revealed the extent of Devonian rocks to be smaller than had been supposed; paleontological studies revealed that much that had been considered Devonian in pre-Revolutionary times was really Cambrian, Ordovician, and Silurian. The lithology of the Devonian, however, turned out to be more diversified than had been supposed previously; the period saw the deposition of clays, sandstones, conglomerates, lavas, tuffs, and breccias, as well as shales and limestones. The Devonian sequence contains, however, terrigenous deposits in addition to the marine sediments and effusive lavas; these show that portions of the region were raised during the Caledonian Revolution. This is borne out by the presence of volcanic lava flows, by the lithology of the sediments, and the character of Devonian flora that made their appearance early in the period.

A well-developed, richly fossiliferous Carboniferous sequence (that carries abundant fauna and flora) is represented by marine, lagoonal, and terrigenous deposits that indicate a continuation and spread of the emer– gence initiated in Devonian time. (The extent of emergence is measured by the extent of coal.) The lithology of the Carboniferous is even more diversified than that of the Devonian; claystones, coals, gypsum, and limonite appear in the stratigraphic column together with the characteristic limestone, shales, marls, sandstones, and conglomerates. Lavas, volcanic breccias, and tuffs of lower and early-middle Carboniferous age are found throughout the region, but upper Carboniferous extrusives are confined to it southeastern portion.

Recent studies have established the presence of Permian formations in Kazakhstan; this series is represented by the Kalbinsk Range coal deposit, the Kenderlyk oil-shale deposits in the Saur Mountains (these carry a fish and pelecypod fauna), and the fossil-bearing marine formations on the shores of Lake Zaisan-Nor. The fish and pelecypod fauna in the copper-bearing sandstones that lie unconformably upon the Carboniferous rocks in central Kazakhstan fix the age of the former as Permian.

These Paleozoic faunas and floras were classified and described, in part, by a number of Soviet paleontologists, including, in particular, Gorski ^ ,^ Krishtofovich, Nalivkin, and Nekhoroshev.

No Triassic rocks have been observed in Siberian Kazakhstan, and it is improbable that any will be found, inasmuch as the Permian marine sediments do not extend west of points east of Lake Zaisan-Nor. The sea had retreated eastward, and only embayments reached westward to the Irtysh valley. The Permian formations are terrigenous over the rest of the region. The Cheliabinsk

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Basin coal measures, however, are uppermost Triassic (Rhaetic). The entire region consisted of dry land through the upper Permian, the Triassic, and the Jurassic, and it was only in late Jurassic time that a marine trans– gression moved southward, parallel to the Urals piedmont.

The Jurassic is represented by sandstones, shales, claystones, con– glomerates, and a variety of plant-bearing coal deposits, as well as the fossil clays and bauxites of an ancient zone of weathering; these lie here and there unconformably upon Paleozoic rocks. The cola deposits of Karaganda, Dzhezkaggan, Kiakta, and Baikonur are of Jurassic age; they lie on top of Permian rocks at Kenderlyk and at some points west of the Irtysh.

Lower Cretaceous marine formations crop out north of the Aral Sea; Upper Cretaceous formations crop out along the eastern margins of the Turgai Depression, and also appear in the vicinity of Pet ^ r^ opavlovsk on the Depression’s northern slopes. (This information was discovered by means of drilling.) In central and eastern Kazakhstan, Cretaceous red conglomerates and finer grained sedimentary rocks fill ancient valleys and underlie early Cenozoic formations.

Red, yellow, and white Tertiary conglomerates, sandstones, marls, clays, kaolins, sands, and gypsums are found in ancient valleys and depressions. In places these formations form lines of hills (in the vicinity of the Saur Mountains), or form divides between valleys, as along the Black Irtysh or in the Golodnaia Steppe (at Bedpak-tala). There are localities, for example, Mount Ashu-tas along the Irtysh, at which a rich Oligocene-Miocene flora is found. Other localities carry remains of upper Oligocene, Miocene, and Pliocane vertebrates, and still other localities carry symptoms of Tertiary marine conditions.

The regional Quaternary is represented by deltaic, overbank, rainwash, and stream-bed deposits. These include forest soils, gravels, sands, and clays of river terraces; as yet, these deposits have not been investigated thoroughly. Manual remains are found occasionally.

A variety of intrusive bodies and veins connected with a number of tectonic movements have invaded the pre-Cambrian and Paleozoic formations in the region. Basic and ultrabasic rocks are the hallmark of the pre-Cambrian here, and two alkaline granite intrusions associated with two tectonic move– ments are present. The Salair and Teconic phases of the Caledonian Revolution were accompanied by the injection of granodiorites, while the upper Silurian phase saw the injection of great volumes of basic and ultrabasic rocks. Early Variscan movements were accompanied by granodiorite and biotite-hornblende intrusions (mid-Carboniferous), while the injected bodies associated with the later Permian phases of the Variscan orogeny consisted of alkaline granites and other alkaline rocks (nepheline syenite, te a ^ s^ chenites, pantellerite, anorthoclase ^ -^ rich rock species).

West of the Irtysh these intrusive rocks are replaced by extrusives that cover the lower Permian terrain, and they may be of lower Mesozoic age. The only indication of later volcanism is a group of basalt dikes in the Kalbinsk Range. Other Paleozoic extrusives have been mentioned above; these tend to be alkaline rather than acid.

The structure of the region is the product of two pre-Cambrian tectonic movements, four orogenic stages of the Caledonian Revolution, and four orogenic stages of the Variscan. These structures are the geosynclines, monoclines, and raised platforms that have characterized the tectonics of Kazakhstan since Paleozoic time. Zones of folding have been developed in the geosynclines and,

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to some extent, upon the monoclines; brachyfolds and domes have been developed on the monoclines.

Post-Permian vertical oscillations occurred in the Upper Jurassic, in the mid-Cretaceous after the end of the Turonian epoch, and at the end of Cretaceous time. The marine waters that commenced their advance from the north, along the foothills of the Urals, in late Jurassic and early Cretaceous time, reached Kazakhstan in Tertiary time, and involved the region in the general downsinking, transforming it into an archipelago. Uplift at the end of Oligocene time reestablished dry land conditions. All of the movements associated with the Alpine orogany were vertical oscillations, though fault movements occurred in some places; these latter continued as late as Pliocene time, and even into one of the interglacial stages.

It is worthy of note that the dimensions and distribution of the region’s folded zones is the subject of a dispute between Kassin, who draw the first tectonic ma n ^ p^ of Kazakhstan, and Shatski ^ ,^ who used materials gathered by Academy of Science ^ s^ field parties to draw a different map.

Gornostaev, Eliseev, Kassin, Nakovnik, Nekhoroshev, Rusakov, Satpaev, Shligin, Iagovkin, and Iskovlev have made perhaps the most substantial con– tributions to the study of the geology of the region.

The Altai-Saian region embraces the Altai and Kuznetsk Alatau, the Salair Mountains, and the Western Saian, and the Kuznetsk and Minusinsk basins that lie among these ranges. The western boundary of the Altai-Saian region runs through Novosibirsk district, and the eastern boundary runs through Krasnoiarsk ^ and^ Yenieeisk districts. Formerly, this area was known in the most general way, investigations having been confined to areas that lie along the Trans-Siberian Railway trunk line. The geologists of the Imperial Geological Survey ascer– tained the general nature of the Kuznetsk Basin and the mountain ranges that

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surround it; Survey geologists also explored various portions of the Minueinsk Basin and the eastern slope of the Alatau. The Altai mining dis– trict was known from reports compiled by the district’s many mining engineers, but the only data on the Altai Mountains and the Western Saian consisted of reports of infrequent travelers. After the Revolution, however, the geological investigation of this great and tectonically complex area forged ahead at greatly increased tempo because of intensive prospecting activity by the Western Siberian Department of the Soviet Geological Survey (later the Geological Administration).

Mesozoic and Cenozoic continental deposits, in general, and the great Jurassic coal series of the Chulym-Yenissisk Basin, in particular, dominate the flat and gently rolling areas that constitute the northern portions of the region. The ^ A^ lower [] Carboniferous Minusinsk series, outcrops beneath the Jurassic formations ^ along^ at the ^ southern^ edges of the basin. Pre-Cambrian, Cambrian, Silurian, and Devonian deposits, as well as some igneous rock bodies, are found in an ancient horst structure in the Arga Range near Achinsk, and con– statute the most important outcrop in the Chulym area. Cambrian, Ordovician– Silurian, Devonian, and some pre-Cambrian rocks outcrop in the Kemchugsk Mountains, between Achinsk and Krasnoiarsk. Devonian coals are found on the western shore of the Yenisei River, southwest of Krasnoiarsk. The Jurassic formations are overlain by plant-bearing Upper Cretaceous beds at some localities, and small, widely scattered areas of Tertiary deposits are also preserved.

West of Tomsk, Taiga, and Novosibirsk, a Carboniferous-Permian coal series, Upper Devonian and lower Carboniferous marine sediments, and Cretaceous con– glomerate underlie plant-bearing Tertiary (Eocene and Miocene) and Quaternary

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sediments; massive granites outcrop along the Ob near Novosibirsk.

The region’s pre-Cambrian and Paleozoic rocks are intensively deformed, whereas the Mesozoic and Cenozoic rocks have been subjected to gentle, local, and shallow folding. Late Variscan granite intrusions are also present.

Korovin’s work on the Yenisei-Chulym Basin is notable, as is Vasilev’s work on the Arga Range.

The Kuznetsk Al ^ a^ tau and the Shoria Upland have been quite thoroughly examined by a number of investigators, because rich mineral deposits (gold and iron in particular) are present in the area. Pre-Revolutionary investigators recognized the fact that pre-Cambrian rocks dominate the regional lithology, and belong to a range of rock types that extends from gneisses to a variety of schists. During the early years of the Soviet regime, geologists were inclined to regard all of the pre-Cambrian rocks as metamorphosed Cambro-Ordovician, but careful studies of excellent outcrops along several of the local rivers revealed that wisespread Archean rocks, wedged into early Paleozoic formations by compli– cated tectonic movements, are present, as well as Proterozoic limestones, schists and extrusives. Rocks formed during all three divisions of the Cambrian period (Lowe, Middle, and Upper), with their characteristic faunas, as well as Ordovician rocks and fossil-bearing Silurian rocks, lie atop Archean and algal Proterozoic rock, and constitute the main mass of the Alatau together with the Shorian Upland. The rocks of Devonian age, on the other hand, are preserved in some grabens, but in the main, outcrop with lower Carboniferous formations along the borders of the Alatau and in the Shorian Upland. A Permian coal series, Jurassic forma– tions with plant remains, and Tertiary formations are found along the edges of the Alatau, as well as Jurassic and Tertiary gold-bearing conglomerates. Records of two glaciations, which include a number of glacial lakes, are found in the upper Alatau.

The abundant pre-Cambrian and Paleozoic intrusive bodies in the area consist of pyroxenites, labradorites, gabbros, gabbro-syenites, gabbro– diorites, granodiorites, granites, and “proterobases.” The region’s extrusives (melanophyres) are also of pre-Cambrian and Paleozoic age.

The breaks and unconformities between various formations indicate a number of pre-Cambrian, Caledonian, and Variscan tectonic movements; the exact number of movements is still in dispute, however.

The first folds observable in the Alatau appeared in pre-Cambrian and early Paleozoic time; these were washed into shallow Devonian seas. Later block movements caused folding, intrusion, and extrusion at the margins of the region.

The work done in this region by Bazhenov, Bulynikov, Derbikov, Kuzmin, Lebedev, Monich, Radugin, Usov, and Churakov should be noted.

The Salair Ridge is the southwestern margin of the Kuznetsk Basin. Here, too, more recent prospecting for polymetallic gold, iron, and bauxite deposits brought about intensive geological exploration. Formations of late Proterozoic, Cambrian, Ordovician, Silurian, and Lower, Middle and Upper Devonian enter into the stratigraphy of these mountains; marine lower Paleozoic, marine lower Carboniferous, and terrigenous middle and upper Carboniferous formations outcrop at the margins of the ranges. (The last two types are found in the small Gorlovsk and Eltsov ^ s^ k coal basins.) Devonian rocks also outcrop at the edges of the coal basins. Questionable Meso c ^ z^ oi z ^ c^ deposits as well as Tertiary lake deposits are found at some localities in these areas. The entire regional Paleozoic is intensely deformed and intruded by granites, quartz nordmarkites, oligoclasite^ s^ , albitophyres and diorite-diabases; the Cambrian, Ordovician, Silurian, and part of the Devonian stratigraphic column include lavas and tuffs.

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Materials were also gathered on Quaternary deposits, ancient bau z ^ x^ it o ^ ic^ zones of weathering, soils, and peat deposits.

The complexity of the tectonic structure of the Salair Mountains is cause for considerable disagreement among geologists. Proterozoic, Caledonian, and Variscan geosynclinals folding is clearly present. A thrust along which Cambrian rocks overrode Devonian formations has been identified on the eastern margins of the area. The fundamental tectonic structure of the area is presumed to be a great eastward thrust of Sudetian age.

The Devonian and Carboniferous are intensely folded, faulted, and overthrust in the Gorlovsk Basin. Block faulting occurred in the region during the Cenozoic; these movements, together with weathering processes, gave the Salair its present relief.

The outstanding students of the area are Bolgov, Bulynikov, Derbikov, Lobazin, Lopushinski, Speranski, Usov, and Iavorski.

The Kuznetsk coal basin attracted the attention of a great number of geologists because the earliest Soviet investigations revealed that the volume and quality of the local coals had no equal in the Soviet Union. For this reason detailed maps for a number of mining localities appeared simultaneously with the first general geological map of the region. Butov’s and Iavorski’s over-all reports on the area appeared in 1927, Fomich’s over-all report appeared in 1940, and 1941 saw the appearance of the Kuznetsk Basin Volume of the Geology of the U.S.S.R. in which a number of geologists contributed to a detailed analysis of the area.

The basin separates the Salair Ranges from the Alatau; the Shorian Upland forms a lower southern margin of the basin. Intensely deformed Cambrian, Ordovician, Silurian, Devonian, and lower Carboniferous formations outdrop

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outcrop along the eastern margin of the basin, while slightly disturbed Devonian and lower Carboniferous formations are found to the south and the northwest. The coal deposits occupy the interior of the basin, and represent the middle and upper Carboniferous, lower and upper Permian, Triassic, and Jurassic formations. The degree of deformation of the strata decreases from the margins of the basin inward. Porphyry and disbase intrusions are found in the lower Paleozoic rocks along the eastern margins of the basin, while basalt sills are intercalated in the Triassic and Jurassic rocks, on both sides of the Tom River, in the mountains of the so-called “melaphyr horsehoe.”

Soviet geologists have worked out the detailed straitgraphy of the area. Abundant fossil faunas and floras fix the age of the main coal beds as Carboniferous and Permian, and establish the presence of Triassic and Jurassic sequences that contain coal beds, contrary to the older impression that all the coal deposits are of Permian age.

The structure of the basin has been formed by repeated pressure from the Kusnetsk Alatau on the east and the Salair on the southwest. The Carboniferous, Permian, and Triassic beds are conformable. The first regional folding of the basin is ascribed to the early Cimmerian ^ Kimmeridgian^ epoch of folding since the Jurassic beds lie with mild angular unconformity upon the Triassic. The Jurassic and earlier beds have been more intensely deformed by a later orogenic movement that was accompanied by outpourings of basalts. It has been assigned tenta– tively to a late Cimmerian ^ Kimmeridgian^ orogenic epoch. Overthrusting is quite common along the margins of the basin, but it diminishes toward the central areas. It seems that the region occupied by the Kuznetsk Basin was a quiescent syncline in early Carboniferous time, afte^r^ intense Caledonian and early Variscan folding. The thickness of the sediments and the large number of

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coal beds indicate that slow, spasmodic sinking was the only tectonic move– ment up to the end of Triassic time. Longitudinal faults in the Kuznetsk Alatau and the Salair determined the boundaries of the syncline and facili– tated the downsinking. Finally, post-Jurassic block faulting in both ranges deformed the sediments once more.

Among the many geologists who have worked in the Kuznetsk Basin, the most significant contributions were made by Adler, Butov, Dorofesv, Ergolsk i ^ a^ ia, Kumpan, Neiburg, Usov, Fomichev, and especially, Iavorski. The fossil faunas were described by Pagozin, Khalfin, Chernyshev, and Ianishevaki; the fossil floras were described by Zalesski, Neiburg, Rad i chenk i ^ o^ , and Khakhlov.

The Altai constitutes the southern half of the Altai-Saian region. The southwestern portions of the Altai were known rather thoroughly before the Revolution, inasmuch as mining operations had been conducted there since the seventeenth century; the rest of the area was known only from the occasional writings of travelers. The mining region, because of its economic importance, was the object of intensive study by Soviet geologists. Detailed reports about almost every part of the area exist, but only a few of these have been published. The Altai Mountains have been investigated less thoroughly than any other section, but the discovery of a variety of economic deposits ^ valuable ores^ will necessitate exhaustive studies there as well.

The presence of intensively metamorphosed pre-Cambrian rocks that include small bodies of rock which may be Archean in age has been established; for the most part, however, the pre-Cambrian rocks are Proterozoic and include several thick patches of tillites, that is, metamorphosed boulder clays that point to very ancient glaciations. Considerable thicknesses of Cambrian marbles and fossil-bearing shale are present, but these are overshadowed by the thicknesses

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of Ordovician and Silurian fossil-bearing shales and limestone roofs. Smaller thicknesses of Devonian terrigenous marls and red sandstones lie unconformably upon the pre-Devonian sequence of rocks. In the valleys of the Bia and Chuia rivers, to the northward, narrow, squeezed-in bands of lower Carboniferous and Permian coal-bearing formations are found. Patches of coal-bearing rocks of Tertiary age are found along the Chuia and Argut rivers.

The geology of the Altai mining district is quite different; the section’s pre-Cambrian and Cambrian rocks have not been examined yet, but it has been established that the dominant local rocks are metamorphosed Silurian, and marine Devonian, Carboniferous and lower Permian. Coal-bearing rocks of Tertiary age have been found only on the Narym River.

A great variety of intrusive and extrusive rocks of various ages con– stitutes an important component of the lithology of both sections of the Altai. A number of granitold bodies are present; these frequently pass over into porphyries. Basic rocks are present in smaller volume. The tectonic structure of the Altai Mountains, also, is different from that of the mining district; in the former section a Caledonian folding that strikes NW. -SE., but swings to a N E.-SW. Strike in the eastern part of the section dominates the Paleozoic structure. The Devonian rocks are less intensely deformed, and the Tertiary formations were disturbed by much more recent black movements.

All of the Paleozoic folds in the Altai mining district strike NW. -SE.; these folds, however, are cut by two zones of crumpling that strike EW. -SE., and follow the faults at the margins of the Paleozoic geosyncline in which great thicknesses of Devonian, Carboniferous, and early Permian sediments accumulated, and were intruded by great bodies of Permian granite.

V. A. Obruchev originally pointed out that the entire folded structure of the Altai was completed in Paleozoic time. The region was almost base– leveled in Mesozoic time. Cenozoic block faulting produced renewed uplift in the region. This fact of block faulting accounts for the occurrence of coal-bearing Permian formations as wedge-shaped outcrops among fault lines, and for the upraised and somewhat folded condition of the local Tertiary formations.

Quaternary and recent glaciations have been studied in the Altai in considerable detail. One, or possibly two, glacial stages have been identi– fied that antedated the Rise and Würm stages; the earliest of the regional glaciations out into a different and less rugged terrain.

The most significant contributions to the store of information on the geology of the Altai were made by Baklakov, Boldyrev, Bublichenko, Origprev, Eliseev, Kotulskii, In. A. and V. A. Kuznetsov, Markhilevich, Nekhoroshev, Padurov, the Tronovs, Churakov, and Shakhov. (The description of the Paleozoic fauna is lagging far behind the geological field investigations.)

The Western Saian is the eastern continuation of the Altai Mountains. Investigations have brought to light a wealth of new data. Red metamorphic rocks of pre-Cambrian age seem to dominate the lithology of the region; smaller sequences of Cambrian, Ordovician, Silurian, and Devonian rocks are also present. Closer scrutiny, however, reveals that the regional Proterozoic component is relatively minor, and that the greater part of the metamorphic and red rocks are Lower and Middle Cambrian and Ordovician. In fact, it is the Cambrian and Silurian formations that turn out to dominate the regional stratigraphy. Three bands of iron-bearing quartzites represent the Silurian period. A Devonian sequence, the Minusinsk series of the lower Carboniferous, and upper Carboniferous– Permian coal-bearing formations are present in the northern foothills. The

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supposed Triassic marine formations along the Us River constitutes a highly problematical case, inasmuch as they were first dated on the basis of a poorly preserved fossil fauna, and the dating was never verified. The intrusive bodies found in the region are of Caledonian age, and possible pre-Cambrian. A belt of Salair (Upper Cambrian) serpentines constitutes an ultrabasic component of the regional lithology. The local extrusives are said to be mainly Silurian. An examination of the local Quaternary formations indicates two glaciations.

The tectonics of the Western Saian are as follows: The Variscan orogeny compressed and overturned Cambrian and Ordovician folds that had been thrown up in the course of Caledonian movements. These overturned folds were thrust for great distances over upper Paleozoic rocks along the edge of the Minusinsk Basin. Like the Altai Mountains, the Mesozoic and Cenozoic orogeny in the area consisted of block faulting; these movements give the region its present rugged relief.

The greater part of the material on the geology of the Western Saian has been collected by Bazhenov.

The Minusinsk Depression is bounded on the west by the Kuznetsk Alatau, on the south and east by the Western Saian, and on the north by the Eastern Saian and the Solgon R ^ r^ anges. The presence of copper, iron, gold, and asbestos deposits attracted the attention of pre-Revolutionary geologists to the region. Soviet geologists have continued the study of these deposits, dis– closed the existence of now economic ^ other^ deposits, and indicated the possible presence of oil pools and salt. Maps have been issued and a great deal of information collected, but several important problem still remain unsolved.

Two ranges that trend ENE. -WSW. divide the Depression into three basins. Pre-Cambrian and lower Paleozoic rocks outcrop in the ranges; middle and upper Paleozoic rocks occupy the basins. The Proterozoic period is represented by limestones, graywackes, and siliceous slates; the sediments are intruded by

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granites, gabbros, and porphyries. (A number of investigators regard this sequence as Cambrian.) The limestones carry algae and erratics that were presumably dropped from icebergs during a glacial epoch. The local Middle and Upper Cambrian limestones contain algae and a fossil fauna, and are intruded by diabases and porphyries. A series of tuffs and porphyries is tentatively dated as Silurian. The sea retreated from the area in Silurian time, but returned for a short time in the Devonian. The Lower Devonian rocks are red plant-bearing sediments and effusive; the Middle Devonian sequence begins with plant-bearing oil shales, while limestones with a marine fauna constitute its upper portion; the Upper Devonian rocks are red terrigenous sediments with fossil r ^ f^ ish remains and plants. The Minusinsk series, which some writers regard as lower Carboniferous and others as Upper Devonian (on the basis of the fossil plants present), overlies the major Devonian sequence. The Minusinsk series, in its turn, is overlain by a coal-bearing series the age of which is still in doubt (upper Carboniferous or lower Permian). Coal-bearing Jurassic rocks are found in the northernmost basin. Tertiary deposits are minor. The Quaternary period is represented by sands and loosses that contain plant remains and human artifacts.

It is doubtful whether Proterozoic folding movements took place in this region as there does not seem to be a regional break between Proterozoic and Cambrian sediments. The Caledonian folds have clearly geosynclinals character and are contemporaneous with adamellitic and basic intrusions. Variscan movements produced en e ^ é^ chelon fold and domes in the basins of deposition where Devonian, Carboniferous, and Permian sediments had accumulated. The major faults at the margins of the depressions (occasionally associated with thrusts and extrusives) had their origin in Caledonian movements, but are

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largely the products of Variscan orogeny. The Jurassic beds in the northern– most basin were deformed during a later orogeny.

The chief contributors to the geological literature of the Minusinsk Depression are Bulynikov, Vologdin, Domarev, G. A. Ivanov, Krubetov, Churakov, Shamanski and Edelshtein. Gromov’s and Sosnovakii’s studies of the region’s Quaternary formations are noteworthy.

The Siberian Platform is bounded by the Eastern Saian on the south, by the Yenisei Ridge on the west, and by the Taimyr Peninsula on the north. Formerly, adequate data were available only on sections that lie in the southern quarter of the Platform along the Trans-Siberian Railroad, in the Yenisei gold mining district, along the Lena River, and in parts of the Viliui River basin. The rest of the area was known only from the reports of occasional field parties, and some of them very old. Recent investigations were carried out in the coal fields of the Irkutsk, Kan, and Tunguska basins, the Angara-Ilim iron district, the Norilsk pyrite deposits, the Viliui and Gulf of Khatanga rock-salt deposits, and the Yenisei gold fields. The wartime discovery of oil-trap structures in the Anabar Massif, the Viliui Basin, and the Severnaia Zemlia Islands attracted a number of geologists to these areas. Thus, virtually the entire Platform has been investigated, and even the Eastern Saian, long a blank spot upon the map, has seen the day of its geologic mapping.

The pre-Cambrian foundations of the Platform outcrop, at the margins, in the Yenisei Mountains ^ Ridge^ , the Eastern Saian, the Cis-Baikal ^ Cisbaikal^ R ^ r^ anges, and the Anabar Massif. The last-named massif, incidentally, was discovered by the Baklund-Tolmachev expediton of 1905-1907, but is was not described geologically until recently.

It is made up of Archean charnockite gneiss, granulites, and amphibolites. These metamorphic rocks have been intruded by granite bodies and associated

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offshoot veins, and basic dikes. Archean and Proterozoic rocks also outcrop in the marginal areas which we shall discuss presently, and there is no reason to doubt that they underlie the entire Platform. Cambrian, Ordovician, and Silurian rock lie unconformably upon the pre-Paleozoic complex. They have been studied by geologists in various degrees of detail. Lower, Middle, and Upper Cambrian formations have been found on the Platform; the Middle Cambrian limestones dominate the stratigraphic sequence of the Cambrian. Calcareous and red-colored Ordovician and Silurian formations follow, the latter indicating a withdrawal of the sea in the northern portion of the Platform. This conclusion is supported by the fact that the Devonian forma– tions in the Bakhta, lower Tungueka, and Kureika River valleys, near the Yenisei River are colored red also. A Givetian (late Middle Devonian) marine sequence is also found in the Bakhta Valley, however, and Frasnian (Upper Devonian) limestones that carry corals and brachiopods are found in the Kheta River basin. The mid-Devonian marine transgression does not appear to have penetrated very far to the south. Fossil-bearing lower Carboniferous (Tournaisian) marine strata are found along the Kureika and Tunguska rivers. The sea retreated a great distance to the north in lower Carboniferous times, and land conditions prevailed on the Platform from Visean through Liassic time.

The terrigenous upper Carboniferous and Permian Tunguska series lies uncomformably upon early and mid-Paleozoic formations. It extends southward along the Angara River, and almost reaches the Eastern Saian in the Kan River basin. A study of the Tunguska series was not undertaken until recently, when it was separated into the productive, the r ^ t^ uff, and the lava-tuff divisions. These investigations also revealed data on the fossil flora, the coal and graphite deposits, and the olivine-diabase trap intrusions and extrusions.

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The major area occupied by the Tunguska series has been termed the Tunguska Basin and contains vast coal and graphite deposits. It extends eastward into the Viliui River basin, as far as the Chona Rive.

Jurassic beds lie upon Paleozoic in the eastern portions of the Viliui River basin; these were identified by Rzhonenitskii before the Revolution, but have been studied in detail recently by geologists. The Lower Jurassic formations are fresh-water sediments, the Middle Jurassic formations are marine (ingression by seas from the north), and the Upper Jurassic formations are terrigenous and coal-bearing. These rocks extend to the southern Lena Valley, where studies of the coal deposits have been made between Kangalas and Bulun. Farther north along the arctic littoral, Lower, Middle, and Upper Triassic outcrops have been studied in the lower Olen s ^ e^ k River valley, east of the Gulf of Khatanga. Rhaetic-Liassic deposits that carry a fossil flora are overlain by a later Jurassic marine sequence which, in its turn, is overlain by coal-bearing Cretaceous sediments. This sequence is found farther west, in the Khatanga Depression. Marine Devonian formations that overlie early Paleozoic sequences are found to underlie Mesozoic strata at Solianaia Sopka. This area contains deposits of rock salt ^ ,^ and pools of oil trapped ^ natural gas, and oil.^ against e ^ S^ alt domes ^ are numerous.^

A Jurassic terrigenous sequence that contains deposits of coal and jet lies directly upon early Paleozoic formations in the southern half of the Platform (in the so-called Irkutsk Amphitheater). This sequence was studied in the Irkutsk and Kan River basins (the Tunguska series outcrops at the margins of the latter section), as well as in the less extensive Khakherei Basin farther north, where oil shales and coals are found. Tertiary terrigenous deposits are rare on the Siberian Platform. The deposits at ^ of^ Quaternary age

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EA-I. Obruchev: Geology in Russia ^ of Siberia^

found in the southern sections of the platform have been studied in much greater detail, because of the presence of building materials there. Two glacial stages have been identified in the northern part of the Platform (the Tunguska Basin), and three glacial stages, plus two interglacial marine transgressions from the north have been identified in its northeastern sections.

Except for the extrusive rocks in the pre-Cambrian complex in the Anaber Massif, traps are the only rocks of this type on the Platform. The main concentration of traps is in the Tunguska Basin, but they are also found in the Viliui River basin, to the east, and in the Irkutsk and Kan River basins, to the south. The main outpourings of molten lavas occurred in Permian time, but bursts of igneous activity occurred in Mesozoic, and possibly even Tertiary time. Attention may be called to the A ^ a^ lkali gabbro intrusions along the Kheta River which are composed of ijolites and melteigites, and associated extrusives chiefly augi i tic, melilitic, and limburgitic basalts; the age of these igneous rocks is probably late Mesozoic.

Tectonically, the Siberian Platform is a great area of undisturbed Paleozoic rocks that are deformed only at the Yenissi, Eastern Saian, and Cis-Baikal ^ Cisbaikal^ margins, where the strike of the folding parallels the strike of the pre-Cambrian outcrops. The Cambrian rocks are slightly raised at the margins of the Anabar Massif. The structure of the interior of the Platform consists of extremely gentle folds in the Paleozoic rocks; rarely does one see such gently rolling structure. Movements in the basement complex, however, have generated shallow basins in the Viliui, Yenisei, and Saian sections Both the Tunguska series and the Jurassic strata are folded in the Viliui Basin, and at some points in the Irkutsk Basin. The main folding on the

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Platform was of Caledonian date, though the Variscan Revolution produced folding and faulting in the Tunguska Basin; the traps poured out along the faults produced at that time. The Mesozoic era was a time of regional oscillations that brought in Jurassic seas from the north and formed lakes in the south; some weak folding also resulted. Oscillation continued into Tertiary time.

The contributions of the following geologists stand out among the many studies conducted in the area: A. I. Gusev, A. A. Grigorev, Zhemchughnikov, Zegebart, Korovin, Levinson-Lessing, Maslov, Moor, S. Obruchev, Otten, V. Sobolev, Tebenkov, Frishenfeld, and Iarahemeki.

The Yenisei Mountain ^ Ridge^ north of the Angara River had been investigated in considerable detail previously; the southern third of the mountain system (south of the Angara) was known only roughly, however. Soviet research concerned itself with the entire mountain system. A great Proterozoic sequence that consists of series of metamorphosed slates, quartzites, and limestones, topped by tillite, has been established here. Archean gneisses and schists dominate the lithology south of the Angara River. These rocks outcrop at some localities north of the Angara also; in any event, they are close to the surface here. Local sequence of Lower Cambrian red sediments, conglomerates, and sandstones are found, and Cambrian, Ordovician, and Silurian deposits outcrop along the flanks of the mountains. The Archean and Proterozoic rocks are intruded by granite bodies and associated veins. Islands of coal-bearing Jurassic rocks are found in the central third of the mountain system. Evidence of weak glaciations is found in the north.

Proterozoic folds strike NW. -SE. and cut the Yenisei River at an acute angle. Caledonian folds of Cambrian, Ordovician, and Silurian strata are

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pressed against both sides of the mountain system and faulted on a major scale.

Gornostaev, In. Kuznetsov, I. G. Nikolaev, S. Obruchev, and Shchukin are probably the leading students of the era.

The Taimyr Peninsula is separated from the Siberian Platform by the Khatanga-Yenisei Depression. The area was hardly known before the Revolution, and the adjacent Severnaia Zemlia Archipelago had just been opened. Outcrops of pre-Cambrian granites, gneisses, mica schists, phyllites, and cherts are found along the arctic coasts. Farther south these metamorphics are replaced by outcrops of Ordovician and Silurian formations and rocks of the Tunguska series with intruded traps. This complex constitutes the Byranga Plateau. The Piasina River basin, to the west, is made up almost entirely of coal-bearing formations of Tunguska age; marine deposits of Cretaceous age are also found along the Yenisei River in this area. Upper Devonian (Fraenian) and lower Carboniferous formations outcrop in the Efremov a ^ s^ k uplift section; the basal Tunguska beds are marine here. Lower Cambrian conglomerates cover the Proterozoic metamorphosed slates on the Cheliuskin Peninsula, while all three divisions of the Cambrian period are represented in the Severnaia Zemlia Archipelago. The Quaternary period is represented by the moraines of two glacial advances and the sediment laid down during one interglacial marine transgression from the north.

There is considerable disagreement about the tectonics of the Taimyr Peninsula. Early investigators in the area thought that a great thrust movement had moved a mass of crystalline rocks over an Ordovician-Silurian terrain, and had thrust the overridden Ordovician-Silurian rocks over a Tunguska series terrain. The fault system was supposed to strike ENE.-WSW. Subsequent investigations, however, have shown that the Caledonian folds were

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overturned to the south, and that the regional fault system is characterized by smaller displacements and is of Variscan origin. The folds swing to a NE.-SW. and N.-S. strike on the Cheliuskin Peninsula, and assume a NNE.-SSW. and NW.-SE. strike in the Severnaia Zemlia Archipelago; thrust faulting complicates the structure in the latter section. The main orogeny in these areas is also Caledonian and was accompanied by the intrusion of granite bodies; the Variscan movements were accompanied by intrusion and extrusion of trap. Mesozoic and Cenozoic movements were oscillatory.

Aller, Anikeev, Baklund, Liutkevich, Mutafi, Smirnov, and Urvantaev have made significant contributions to the study of the geology of the Taimyr Peninsula.

The Eastern Saian was as little known as the Taimyr Peninsula. Investi– gation of the area was undertaken on a large scale in the middle 1930’s; geological maps published in 1934 still contained large blank areas. The now data indicate that Archean gneisses and amphibolites dominate the lithology of the region. Proterozoic phyllites, sandstones, and limestones are second in importance; these have been grouped into three series. The aggregate thickness of the Proterozoic rocks is twenty kilometers (66,000 feet). Cambrian shales, phyllites, sandstones, and limestones with subordinate tuff and lava beds are present, in which an early and Middle Cambrian fossil fauna has been found. The uppermost strata of this sequence may be Ordovician, however. The volcanic rocks are generally taken to be Silurian-Devonian. Marine conditions terminated in the Western Saian in Cambrian, or at the latest, in Ordovician time. The Devonian period is represented by terrigenous red sandstones and conglomerates of small thickness and lateral extent. At two localities plant-bearing Jurassic lake deposits rest directly upon an eroded

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pre-Cambrian surface. The Tertiary period is represented by conglomerates that contain argillite lenses with Miocene plant remains. Those are over– lain by a Quaternary basalt-moraine-basalt sequence.

The tectonic structure of the Eastern Saian is the product of Archean and Proterozoic orogenic cycles; these included acidic and basic intrusions and extrusions. There was no Caledonian geosyncline in the southwest, and the northeastern portion of the region was part of an uplifted plateau. The pre-Cambrian folds strike NW. -SE. whereas the Caledonian folds to the west strike N W ^ E^ .-SW. In Devonian time, land bridges that connected the entire Saian to the Siberian Platform existed. Subsequently, the only tectonic movements that occurred in the area were faulting, monoclonal flexuring, and stage-by-stage regional uplift. The present relief of the region was determined by basalt flows that filled the valleys in Quaternary time. Subsequent studies have shown that previously inferred thrusts do not exist in the region.

Bazhonov and Vologdin have done valuable work at the western end of the mountain system; Konoplev, Molchanov, S. Obruchev, and N. Scbolev made the most significant contributions to the geology of the greater portion of the system, and S. Obruchev, after a three-year study, synthesized and interpreted the tectonic and stratigraphic data of the region.

The Baikal Shield (the Ancient Roof of Asia), the Alden Shield, the Stanovoi Mountains, and the Eastern Trans -B ^ b^ aikal . Some parts of this region were thoroughly known before the Revolution, other parts were known incompletely, and still others were altogether unknown. The southern half of the Trans -B ^ b^ aikal was studied by a great number of field parties in connection with the construc– tion of the Trans-Siberian Railroad; the northern half was less intensively

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studied. A map (1 ^ :4^ 2,000) of the Lena gold mining district and the Bodaibo and Vacha River basins was based on the data gathered by a particularly large number of field parties. The greater part of the area was not well known at all, however, and the entire Aldan River basin, the Stanovoi Mountains, and the area east of the Vitim River were known only from the reports of occasional travelers. Local areas in the northern, central, and southern Cis -B ^ b^ aikal had been thoroughly studied, but only fragmentary inform– tion was available about the rest of the area, as well as about the western Khamar-Daban Mountains between the headwatersof the Dzhida River and the Mongolian border.

Considerable advanced have been made in the geological study of the area but these recent studies have not been uniformly intensive and have not covered the entire region. The southern half of the eastern Trans -B ^ b^ aikal and various portions of the western Trans -B ^ b^ aikal, the Cis -B ^ b^ aikal, the Lena section, and the Aldan Plateau have been thoroughly investigated; the other sections of the region less thoroughly. If one judges by available literature, our knowled ge of other parts of this vast region has not advanced beyond the pre-Revolutionary scope of information. Unfortunately the reports of many field parties have never been published; these probably contain much supple– mentary material. The fact that publication lags considerably behind field research limits our knowledge and hampers geologists. This lag, incidentally, is not peculiar to the area under discussion but applies to all Siberian geological literature; the delay is worst of all, however, in the case of the eastern and northeastern areas.

The various sections are discussed separately, from west to east.

The Cis -B ^ b^ aikal has been most thoroughly studied in the valleys of the

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Buguldeika, Anga, and Sarma rivers, in the Lena Valley, and in the vicinity of Cape Elckhin. The presence of Archean, Proterozoic, and Lower Cambrian forma– tions has been established here. The Archean rocks have been grouped into three divisions as have the Proterozoic; the Lower Cambrian formations, on the other hand, have been divided into two units. The upper Proterozoic rocks, which have been further grouped into the Colousten, the Uluntuisk, and the Kachergat series, lie unconformably upon lower and middle Proterozoic rocks. The g ^ G^ olousten, Uluntuisk, and Kachergat series are not Cambrian, as had been thought previously. The Cambrian sequence consists of the Motsk conglomerates and the Ushakov series; it lies unconformably upon the Proterozoic rocks. The region’s pre-Cambrian intrusions have been studied. Middle Cambrian limestones and Upper Cambrian red sediments that merge upward into Ordovician formations are found in the mountains in the western part of the section.

An early Quaternary river system that drained westward, rather than into Lake Baikal, has been discovered; the reversal of drainage, of course, indi– cates recent downsinking of the lake. Two glaciations have been identified in the Primorskii Mountains, to the north.

The Archean and early Proterozoic folds in this section strike ENE.-WSW., that is, across the strike of the Lake Baikal structural depression. The folds of upper Proterozoic age, on the other hand, strike NW-SE., while the Cambrian folds strike again NE.-SW. and are overturned to the northwest. Geologists still disagree as to whether the Cambrian folds constitute a marginal zone of rocks that were squeezed against the Baikal Shield from the direction of the Siberian Platform (Suess), or whether the Caledonian orogeny also involved the Proterozoic rocks. The question whether the Archean rocks were thrust over Jurassic formations in the Angara headwaters region by thrust faulting, or by

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reverse faulting, is also in dispute.

Pavlovski ^ ,^ Tsvetkov, and, in part, Katnshenok made the most significant contributions on the geology of the central section of the region, Arsenev and Maslov on the northern section, and Ge rv ^ vr^ ussvich, Dumitreshko, and Kolenko on the southern section.

The Baikal Upland has not been studied very thoroughly. Investigations have established Archean rocks and a thick Proterozoic sequence that has been grouped into several divisions. (These Proterozoic formations border upon an area of Lower and Middle Cambrian outcrops.) The contact between Proterozoic and Cambrian rocks has not been exactly determined and is currently the subject of dispute (Ditmar, Dombrovski ^ )^ .

An area of old mica deposits along the lower course of the Mama River has been studied thoroughly. Pegmatite dikes out crystalline limestones and schists in a great syncline in a granite terrain (Markov, Misharev). Much of the area between the Mama and Angara rivers remains unexplored. Dumitrashko, however, has made geomorphological studies in the vicinity of the Angara River. He has also collected new data about the Archean, Quaternary, and late glacial deposits in the area.

The Lena gold district has seen a renewal of geological investigation only recently, be means of field parties sent out by the Nigrizoloto and Zolotorazvedka Gold Prospecting Agency. The first studies of the presumably Proterozoic rocks in the valleys of the Bodaibo, upper Vacha, Nygra, and Kadal rivers have led to a grouping of the rocks into four division. An unconformity separates the second divisions from the third, and an as yet unidentified fossil fauna has been found in the lowest division. Two ancient erosion surfaces and several Quaternary formations have also been identified.

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EA-I. Obruchev: Geology of Russia ^ Siberia^

Geologists tended to deny regional glaciations at first, but new data indicate that glaciations has occurred. Zolotorazvedka field parties have identified the morainal deposits of two glaciations of uncertain age in the northern portions of the Zhuia River basin. Field parties of the Geological Scientific Research and Development Institute (gold section) have divided the Middle, and especially the Lower, Cambrian sequence into a number of units along the lower courses of the Vitim and Bolshoi Patom rivers at the borders of the Starostin district. Klevenskii, who worked along the Mal ^ y^ i Patom and Molvo rivers farther east, proved the existence of a thick Lower Cambrian sequence; the sequence includes cong ^ l^ omerates that carry granite and gneiss fragments. Klevenski has also described a thin sequence of Middle Cambrian limestones, and a great thickness of Upper Cambrian redbeds. These findings are confirmed by Areenev’s, along the lower Olekma, farther east, where the thickness of the Lower Cambrian sequence is 800 meters and that of the Middle Cambrian sequence 75 meters.

Gerasimov has described the granites of the peak between the Ugakhan and Nygra rivers on the basis of old data, and analysed their relation to the local placer gold deposits. He assigns an early Cambrian date to the granites.

As regards the tectonics of the area, the latest investigations have shown that the metamorphic rocks in the southern portion had been subject to intense and complicated folding and that the Cambrian formations on the eastern and southern margins are also strongly folded.

The western Trans -B ^ b^ aikal has been described quite thoroughly in a great number of hitherto unpublished reports. This is particularly true of the Ba t ^ r^ guzin section. We note, however, the publication of Eskola’s work on the Sviatoi Nos [: ] and the upper B o ^ a^ rguzin River valley; this treatment is

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based upon the Finnish geologist’s pre-Revolutionary observations, and describes and interprets the Archean of both areas and the Proterozoic rocks of the Barguzin Valley. Meister, Polovinkina, and Svitalskii have described the geology of the northern Mui Mountains and the Vitim Plateau; these geologists, like Eskola, based their treatment upon old data. Carusevich and Zaklinskaia gathered new data on the geochemistry of the Archean rocks in the Turka River basin. Pavlovski described the Archean, Proterozoic and Cambrian tectonics, and the plentiful evidence of glaciations in the central Vitim Upland. Arsenev investigated the central portions of the Vitim Valley; he presented data on the tectonics, effects of glaciations, the upper Proterozoic and Jurassic stratigraphic sequences, the granite intrusions, and the pre– Cretaceous and Quaternary basalts.

Shatski has found a high-angle reverse fault that moved pre-Cambrian over folded Jurassic rocks at the Selenga headwaters; he correlated it with reverse faulting at the mouth of the Angara River. Tetiaev and Vasilevskii studied the vicinity of the Pitatelevskii Springs. Tetiaev led a field party into the neighboring Khamar-Daban and upper Udinsk region, where they mapped the outcrops and the structure of the metamorphic, late Paleozoic and Mesozoic formations, and established a post-Jurassic age of most of the granite intrusions. Florensov and Larin investigated the coal series at Lake Gusin and grouped the terrigenous strata into Upper Jurassic, Lower Cretaceous, and Tertiary sequences. The Jurassic folds strike N W ^ E^ -SW. here and Archean rocks are thrust over Jurassic in the Monostoi Mountains. Arsenev investigated the coal-bearing Tertiary series on the southeastern shores of Lake Baikal; later, Riabukhin studied the sequence in connection with a local oil-prospecting program. Palibin described the local Tertiary flora.

A number of geologists — Garusevich, Korzhenskii, Pilipenko, and Smirnov — have investigated the Sliudianka P ^ p^ hlogopite deposits. The local Archean rocks and the pegmatite dikes that cut them have been described. Pilipenko found that the effects of glaciation in the Khemar– Daban Mountains extend almost to the water level of Lake Baikal. Prokopenko and the Lomakin Brothers crossed this range in its southern portion, between the Irkut River basin ^ plain^ and the headwaters of the Dzhida River. They mapped the outcrops and make-up of the pre-Cambrian and lower Paleozoic sequences, and noted the fundamental features of the basalts that outcrop on the peaks of the range.

In the Dzhida headwaters section, Naletov studies the pre-Cambrian rocks (one sequence carries algae), archaeocyathid-bearing Cambrian formations, the Mesozoic coal series, the Quaternary deposits, the Caledonian and Variscan folds and intrusions, and the younger basalts. Shalsev investigated the central Dzhida Valley and found the same pre-Cambrian and Cambrian sequences, in addition to Jurassic terrigenous beds, six igneous intrusions of various ages, and the tuffs of three volcanic cycles. Vereshchagin had analyzed the stratigraphy and tectonics of the coal series. Bes e ^ o^ va has described the Cambrian tungsten deposits in the Dzhida River. Levitski ^ ,^ Misharin, Smolianinov, Speit, and others have also described these deposits.

Farther east, the Balegin iron ore deposits were investigated by Domrachev and Pavlov, and were found to be sedimentary. Preobrazhenski and Purtov measured the potential output.

In the central Khilka River S ^ s^ ection, Vereshchagin investigated the metamorphic rocks, the uppermost Paleozoic conglomerate series, the Jurassic coal series, the Tertiary formations, the intrusive and extrusive rocks, the younger basalts, and tectonics.

Arsenev encountered crystalline and metamorphic pre-Cambrian and lower Palezoic rocks in the Tsagankhuntei Range, as well as great granitoid bodies and an upper Paleozoic tuff-lava series that is cut by alkali granites and syenites. The syenites go over into grudurite and selvsbergite at the margins. Teschenite loccoliths lift the layers of a Lower Cretaceous coal series at one locality. Necheeva described the alkaline intrusions.

Dengin investigated the central Chikoi River basin, and described the local metamorphic rocks, granites, extrusives, tectonics, and the Gutai molybdemm deposits. Voskresenskii investigated the gold deposits in the Chikoi gold district (as did Malyshev and Staln e ^ o^ v) and studied the morainal and terraced terrain there. The Cutai mining district was investigated by Tataev and Fersman, and Donskoi called attention to the fact that the fossil– bearing local lower Carboniferous sequence rests unconformably upon meta– morphic rocks.

The mineal springs and lakes of the western Trans -B ^ b^ aikal have been described by Butyrin, Gladtsin, Dengin, Nikolaev, Tolstikhin, Frank-Kementskii, and others; Soanovskii described the local paleolithic artifacts.

The Aldan Plateau was known p ^ o^ nly from the reconnaissance data that Zverev gathered along the Maia and Aldan rivers, and from the older data gathered by Middendorf and Meglitski. Recent research, however, has ampli– fied our knowledge of the region considerably. In the extreme wester ^ n^ portion of the region ^ ,^ the Tommot gold mining district was described by Zverev and later by Bakhvalov. The latter described the Archean basement complex, and its intrusives, the Lower Cambrian marine sequence, the terrigenous Jurassic sequence, the subsequent alkaline syenites intrusive and basic dikes, the Archean folding, and the post-Jurassic faulting and block movements.

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Arsenev divided the Archean sequence along the Olemka River into three units. Fastalovich and Petrovskii described two types of gold [] ^ d^ eposits in the L a ^ e^ bedinsk mining district. Korzhenski crossed the plateau as far as the T y ^ i^ mpton River. He investigated the petrography of the Archean rocks and the stratigraphy of the Cambrian and Jurassic sequences, classified the metamorphic rocks according to depth, and reported several varieties of cyanite and corundum.

The gold deposits in Archean rocks between the Aldan and T y ^ i^ mpton rivers were described by Serpukhov. Ivanov and Stoliar discovered and described the Uchurochiulbin gold district. This involved the investigation of the local Archean complex, the very thick Cambrian sequence with its cong ^ l^ omerates and fossil fauna, the basic igneous rocks, and the structure. In the subse– quently discovered Allakhiun ^ Allakh-Iun^ gold district, in the northern portion of the plateau, Bilibin, Baikov, Dzevanovskii, Potebinia, Serpukhov, and others described the Lower and Middle Cambrian, Ordovician, Silurian, Upper Devonian, upper Carboniferous, Permian, and Triassic sequences; the various intrusions and the local tectonic effects of the Caledonian, Variscan, and later orogeny; the gold deposits and the local effects of glaciations. Postoev noted the effect of the latest tectonic movements in his geomorphological analysis of the section. Iakzhin described the plateau’s phlogopit s ^ e^ deposits.

The Stanov i ^ o^ Mountains border the Aldan Plateau on the south. To this day our knowledge of the regional geology is fragmentary. Obruchev drew the inference, from new data that the Stanovoi Mountains are entirely separate and distinct from the Iablonovyi Range. The distinctions are orographic as well as tectonic. Obruchev described the pre-Cambrian and its intrusion, as well as the more recent extrusives and tectonics. Anert compiled the

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older materials on the Tuskan and Mulam river headwaters region, and Korzhenaki i conducted a geological reconnaissance along an Amur-Yakutia route, mapped the more recent intrusive, extrusives, and the tectonic structures, and established the boundaries and litho ^ lo^ gic character of the pre-Cambrian, Paleozoic, and Jurassic sequences.

Florov described the Aian gold district; Vasilchenko described the porphyries, tuffs, and sedimentary rocks of the Ulia River basin; and Leontovich seven Cambrian formations (one fossil-bearing) in the central Mai n ^ a^ Valley, as well as the Cambrian gabbro-diabase dikes and sills, the Devonian and Mesozoic formations, and the granitoids and porphyries along the Sea of Okhotsk coast. Alekseichik investigated the stratigraphy, tectonics, oil possibilities, and oil-shale reserves in the Aim River section. Pavlovski i extended Obruchev’s idea that the Stanovoi Mountains are the upper hinge of the young monoclinal flexure that affects the entire Baikal s ^ S^ hield as far southwest as the shores of Lake Baikal, and as far south as the Mongolian border. Pavlovski i also called attention to the large number of grabens (including the Lake Baikal graben) in the Trans -B ^ b^ aikal region. He also studied the times of origin for the grabens and their similarity to the grabens of Africa, and suggested that the Baikal grabens are downthrown blocks between twin sets of reverse faults rather than the downdropped blocks of rifts, that is, they are the products of horst tectonics.

The eastern Trans -B ^ b^ aikal was known, at first, only from engineering reports on the Nerchinsk district; later on during the construction of the Trnas-Siberian Railroad, Gerasimov and Gedroits made a reconnaissance of the southern portion of the region, and Voznesonski i and Makerov of the northern, More recent research has yielded a great deal of new material, some quite

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unexpected largely from the southern section. The northern portion of the region — the Olekma headwaters and the Ingoda and shilka river valleys — have been explored much less intensively.

Proceeding from m ^ s^ outh to north, the following are the most significant results of geological exploration in the region.

Immediately after the Revolution Zver [] ev, Krektar, Svitlovaki i , and Smirnov studied and described the Nerchinak silver-lead-zinc deposits. Artemev further described the lead deposits; Vardaniants, Doktorovich, Crebnitski i , Sushchinski i , and Tetiaev described the tungsten and precious stones deposits; and Arsenev and Makerov the local gold deposits. Obruchev described the Ilinsk and Evgrafovsk gold deposits on the basis of data gathered in 1912; Savalev described the latter.

Between 1925 and 1929 a number of field parties under Tetisev investi– gated the eastern half of the area. These parties studied the fossil fauna, the marine Devonian sedimentary rocks, the lower Carboniferous sedimentary rocks (formerly regarded as Devonian), and the Permian, Upper and Lower Triassic, Lower and Middle Jurassic, terrigenous Lower Cretaceous, and Tertiary formations. These geologists dated the metamorphic rocks of the section as Paleozoic (unfossiliferous). They also determined that the tectonic development began with recurrent thrusting (“ [] ^ t^ ectonic lamination”) to the southeast. These inferences grew out of comparisons to the nappes of the Alps and western Europe. A reevaluation of regional maps after 1929 showed that these conclusions were wrong; high-angle reverse faulting rather than nappe structure dominates the tectonic picture. These investigations also revealed a smaller area of granite intrusion, the presence of scattered Ordovician-Silurian outcrops, the possibility of pre-Cambrian outcrops, and

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the presence of complicated large-scale folds that strike N W ^ E^ .-SW. associated with a set of north-south folds of Variscan date or at least older than Upper Jurassic. It is possible that Caledonian folds are present also. A considerable portion of the granitic rocks is older than Upper Jurassic and is, in fact, pre-Permian, that is, Variscan age. It has been confirmed that the local neutral and alkaline extrusives are late Jurassic, and the basalts are Tertiary and Quaternary. The upper Mesozoic and Tertiary tectonic movements took the form of upward and downward block faulting that was asso– ciated with volcanic activity, thrusting, and a gentle folding of Cretaceous and Tertiary strata.

These later investigations were carried out by Atlasov, Luchitski i , Maksimov, Maslov, Pavlovski i , Rudnev, D. S. Sokolov, Khudiaev, Shchukin, and others.

Artemev, Kreiter, Smirnov, and others continued their study of the local silver, lead, zinc, tungsten, and tin deposits. A new tin district in the Onon headwaters section has been repeatedly examined and described. Pavlov, Pilipenko, and Lavrovich described the fluorite and gold deposits along the Onon and Unda rivers. Various geologists have described the Chernovsk, Khalbon, and Kharanor coal deposits. The ground water, mineral springs, and hydrolaccoliths of the region were studied by Gladtsin, Dzens-Litovski i , Makorov, Silin-Bekoburin, and Tolstikhin; the salt lakes were investigated by Pavlov; the fossil fauna by Kichigina, Krymgolts, Nekhorochev, Rukhin, and Khudiaev; and the fossil flora by Khakhlov. Sheimsan has synthesized the data on the structure of the eastern Trans -B ^ b^ aikal, and has correlated it with the structure of Mongolia.

Nenadkevich and Khrush o ^ c^ hev studied the bismuth deposits along the Kara

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and Amazar rivers, in the northern half of the region. Gor o^ø^nostaev, Zemel, Rikhin, Khakhlov, and others investigated the gold-bearing quartz and tourmaline veins along the Kara River. The Darasunsk gold and polymetallic deposits were also studied. Eight full reports on the geology of the Bukachachinsk coal deposits are available. The Ushmunsk tungsten deposits have also been described in detail. Efremov, Pavlovski i , and Sobolev have gathered new data in the upper Olekma Valley.

The Amur Region and the Southern Maritime Provinces (Including Sakhalin) . Before the Revolution, a small amount of data about those sections of this region that lie along the Amur and Ussuri railway route was available, and considerable data about the geology of the gold districts along the Zeia, Selemdzha, and Amgun rivers. Incomplete data were also available about the Uda River basin, the Ozornyi (Lake) section, the Sikhote-Alin Ranges, and Sakhalin Island. The coal deposits of western Sakhalin and the small oil deposits in the eastern part of the island had been studied.

Recent development of mining industries and the construction of the Baikal-Amur Railway trunk line has advanced our knowledge of the geology of the region immeasurably. The most thorough studies were made in the Bureia River basin, the Mal ^ y^ i Khingan Mountains, the southern portion of the Sikhots-Alin, the southern portion of the Ussuri section, and Sakhalin Island. In the northern sections of the region, however, the section from Zeia head– waters to the mouth of the Amur remained virtually neglected. The great energy with which the Far East Section of the Soviet Geological Survey carried research forward, in this region, is worthy of attention; since this organization’s headquarters have been moved from Vladivostok to Khabarovsk (when the Geological Survey became the Geological Administration), its activities

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in the Far East have tapered off, and the publication of materials on the region under consideration has ceased.

The Ka ^ A^ mur section was subject to intensive geological investigation because of the presence of gold, schoelite, and antimony deposits along the Zeia River and in the Tukuringra Mountains. These deposits were studied by Ar o sentev, Makerov, Popov, Preobrazhenski i , and others. The tungsten and molybdenum deposits along the Selemdzha-Bureia divide have been investigated by Artemev, Vitgeft, Volarovich, Golubin, Mokin, and others. The iron-bearing quartzites of the Mal ^ y^ i Khingan were studied by Aleksandrov, Vitgeft, Danilovich, Dubrov, Pavlov, Sokolov, and Tkalich. Jurassic and Tertiary coal deposits elsewhere in the section have been examined to a lesser extent. The leading investigators of these deposits have been Arsentev, Bochkovskaia, Bykov, Davydov, Konstantov, Matvcev, Ponomarenko, Skorokhod, Kheraskov, and Shatski i .

Other economic deposits that have been investigated include the Oldoi River platinums, the Bogucha m ^ n^ River fluorites, and the Soiuznoe mineral springs, as well as the effects of glaciation in the Tukuringra Mountains, and permafrost. The geology of the Jewish Autonomous Province has been investigated (Abdulaev, Krishtofovich, Bruk, and Shkorbatov), as have been the geology along the Baikal-Amur trunk line and the region’s soils and swamps. A number of reports on the petrography of the various sections have appeared (Afanasev, Bolshakov, Dominikovski i , Lebedev, Polovinkin, Stron, and Suslov). Brauner, Voronets, Riabinin, and Sokolov have described the fossil faunas of the region, and Krishtofovich, Maslov, Prinada, and Shtempel the fossil floras.

These investigat^ors^ ascertained age, structure, and genesis of previously known and newly discovered economic deposits, and described the geology of the region. The greater part of the regional terrain is found to consist of Archean and Proterozoic rocks; a lesser part of Ordovician, Silurian, Devonian^,^

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and Lower Jurassic marine sequences, terrigenous Upper Jurassic and Cretaceous and Tertiary formations. The pre-Cambrian and Paleozoic rocks contain many intrusives, and the Jurassic sediments have also been invaded by young granites; the latter are still the center of considerable controversy, however. The strike and degree of deformation of pre-Cambrian, Paleozoic, and Mesozoic folding have been clarified. The tectonics of the Mal^y^i Khingan, in par– ticular, have been clarified. Here the pre-Cambrian folds strike N.-S. and the Mesozoic folds strike NE.-SW.; the latter, however, are influenced by the former. Pre-Devonian, pre-Jurassic, Upper Jurassic or Lower Cretaceous, and pre-Tertiary orogenic cycles have been identified, in addition to the pre-Cambrian. The Tertiary folding was gentle.

The Southern Maritime Provinces attracted geologists’ attention because iron and coal deposits exist in the vicinity of Vladivostok and in the Sikhote-Alin Mountains. The northern half of the region, along the Amur and Amgun rivers, and the Ozernyi section between them, has been investigated less thoroughly.

A considerable number of geologists have studied the Permian-to-Tertiary coal deposits in the islands, peninsulas, and coastal areas around Vladivostok, and along the lower Suchan River. The Suchan coal deposits are found at depth. The Triassic, Jurassic, Cretaceous, and Tertiary rock sequences here have been the subject of a great number of studies, both incidental and special; the age of the rocks, of course, was determined paleontologically. The Triassic and Jurassic periods were marked by marine transgressions and volcanism.

Among the outstanding students of the region are Anert . ^ ,^ Vittenburg, Elieshevich, Kozlov, A. I. Krishtofovich, Libus, Pavlov, M. Preobrazhenski i ,

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Prinada, Tkalich, and Shtempel.

To the north, in the Suifun section, Koslov, A. I. Krishtofovich, Pentegov, Precorazhenski i , and Iavorski i investigated the Jurassic coal basin and the iron deposits.

The southern portion of the Sikhote-Alin Mountains contain a number of exploitable deposits in addition to the Suchan coal field. These include the magnetite deposits of the Olginsk-Vladimirsk section, Tetiukhe P^p^oly– metallic deposits, and a number of points at which tin can be mined by open-pit methods. Thus far, gold and oil prospecting has gone forward only on the reconnssance level. The main stock of data on the area has been gathered by Volarovich, Gregorev, Dervis, Danilovich, Ivantishin, Kozlov, A. I. Preobrazhenski, Rusakov, Smirnov, and Skorokhod. Skorokhod and Volarovich wrote a general report on the area.

The Khekhtayr Mountains south of Khabarovsk, along the lower Ussuri River, were first studied by Leontovich, Prinada, and Pek. The Amur River below Khabarovsk was studied by a field party that was sponsored by the Soviet Academy of Science ^ s^ and consisted of Danilovich, Kozlov, and Sokolov. The field party found marine sediments of Triassic, Jurassic, and early Cretaceous age, a Tertiary cola series, and both intrusives and extrusives. Malioranski i explored the northern portion of the Sikhote-Alin between Lake Kizi and the mouth of the Amur, and found that extrusive rocks dominate the lithology. Alekseevski i and Polevoi investigated the iron deposits in the basalt section around Nikol s ^ a^ evsk, and Preobrazhenski i the gold placer deposits along the Limura River. Kazanski i first explored the Ozernyi section, in 1914, but his report did not appear until after the Revolution. Subsequently Efremov and Pavlovski i studied the area and found great thicknesses of upper

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Paleozoic and Triassic sediments, evidence of recent oscillatory movements, and extrusive basalts. Arsentev, followed by Preobrazbenski i and Seregin, investigated the O ^ C^ hlia-Orel lakes, mount Belaia, and Kol River gold deposits. Mikhnovich investigated the Komsomolsk section, and found Middle and Upper Triassic and Lower Cretaceous sediments, and Cretaceous granitoids and young basalts. Bagurin found tungsten and tin deposits at Lake Udyl and along the lower Amur.

The fossil fauna of the region was collected and identified by Vittenburg, Voronets, Kiparisov, Kokkerel, Kruglov, Krymgolts, Martynov, and Riabinin; the fossil flora was described by Zalesski i , Krasser, Krishtofovich, Maslov, Palibin, Prinada, and Shtempel.

The study of the tectonics of the Sikhote-Alin Mountains has not advanced very far. Generally speaking, however, the structure seems to be a pair of major anticlines, the combined width of which exceeds that of the mountain system. The anticlines strike N [] ^ E^ .-SW., and carry large brachyanticlines. The outcrops on the crests of these anticlines consist of early and late Paleozoic rocks, while Mesozoic rocks form the limbs. Cretaceous rocks, deformed less than their predecessors, occupy the s u ^ y^ nclines and are overlain by Tertiary rocks that are even less deformed. The tectonic results of several orogenic movements are superimposed upon one another. The last powerful disturbance took place in the Kimmerian ^ Kimeridgian^ orogenic epoch and was accompanied by granite intrusion. The molding of the geanticline was completed in the Austrian epoch when high-angle reverse faulting and volcanic activity began which continued for some time. The great thrust from the southeast postulated by Tetiaev and a number of his colleagues does not exist.

Sakhalin Island was rather well known geologically before the Revolution,

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but more detailed studies of the island have been made since that time especially in the coal and oil regions. An intensive study of well sections, cross sections and paleontological data led to a detailed knowledge of the marine, terrigeonous, and extrusive Cretaceous and Tertiary rocks that make up most of Sakhalin. The coals and geology of the western shore have been studied by Vitgeft, Volkovich, Gapeev, ^ I^ latov, Krishtofovich, Polevoi, and the Japanese geologists Yabe and Shimitsu. The petroleum deposits of the western shore were investigated by Bunin, Krish ot ^ to^ fovich, and Shcherbakov, and the main pools, on the eastern shore by Abazov, Gedroits, Damperov, Kobziashi, Kosygin, Mironov, Perfilev, Polevol, Tanasevich, Khomenko, and others. The two interior mountain chains, which include Paleozoic rocks and contain gold deposits, have been studied by Vitgeft, Eliscev, Krishtofovich, and Khomenko; Smekhov, Khmolev, Khomenko, and Shakhov investigated the geology of the Schmidt Peninsula.

The fossil fauna of the island was investigated by Argomakov, Voloshinov, Gayaseka, Nagao, Chernyshev, Khomenko, and Isbe, and the fossils flora by Krishtofovich and Poiakrov. Krishtofovich, Polevoi, Sokolov, and Tikhonovich wrote a general treatment of the geology of the island.

According to Pleshakov’s recent study, Sakhalin Island is made up of folded geosynclinals sediments of late Cretaceous and Tertiary age. Six stages of the Alpine orogeny are discernable; the Kamchatkan disturbance, between the Upper Cretaceous and the Tertiary; the Kurilean disturbance, between the Oligocene and Miocene; the Amurian disturbance, between the middle and late Miocene; the Tatarian disturbance, in the upper Pliocene; and the Okhotsk disturbance, in Pleistocene time. The island has been sinking since the latter half of the Pleistocene time. The folds are overturned to

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both east and west, and are associated with faults and thrusts.

The Northeastern Region includes the upper Verkh ^ o^ i nsk ^ ansk^ -Kolyma section, the Chukotsk-Anadyr section, and the Kamchatka ^ P^ eninsula. This was the least known portion of Siberia. The only available data about the region consisted of the reports of occasional travelers; some of these were very old. After the Revolution the Northern Sea Route Administration whose ships — the region’s only source of supplies — round these coasts, undertook geo– logical investigations. The discovery of precious metals, coal, and petroleum started a study of the entire area.

The Soviet Academy expeditions to Kamchatka and the founding of the Volcanological Station there laid the foundations for the systematic study of the only part of the Soviet Union where active volcanoes exist. Unfor– tunately, the reports of the field parties that worked under the auspices of the Kamchatka Trust, and the Daletroi (q.v.) organization that succeeded it, have never been published.

The Upper Iana ^ Verkhoiansk^ -Kolyma section include ^ s^ the great ^ vast^ Iana, Kolyme^,^ and Indigirka river basins. Before the Revolution parts of the region had been visited by reconnaissance parties under Wrangel, Toll, Volosovich, Maidel, Tolmachev, and Cherski i . Vast areas, however, remained unknown.

All of the mountain ranges which separate the river basins have been studied since, and these investigations resulted in the discovery, by a party under S. V. Obruchev, of a great mountain system between the Indigirka and Kolyma river basins. This system, which was named the Cherski i Mountains after the geologist who first crossed it at a point at which its extent and elevation cannot be seen, consists of several ranges of rugged relief which shelter small mountain glaciers. The basins of the section’s most important

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rivers were studied, as were several less important upland areas along the arctic littoral, and several river divides along the Okhotsk littoral to the south.

A considerable number of geologists have investigated the Verkhoiansk Mountains recently. A. A. Grigorev laid the groundwork for these investiga– tions when he crossed these mountains in their central portion. Thereafter geologists turned their attention to the old silver- and lead-mining districts in these mountains, and to the Orulgan and Kharsulakh Mountains farther north, In the latest phase of the study of the area, geologists have ventured into the mountains to the south of Grigorev’s route. The northwestern portion of the area has been found to consist of a uniform series of Permian, Triassic, and Jurassic sandstones. (One member of the local Permian sequence carries a fossil flora.) Cambrian, Ordovician, Silurian, Devonian, and Carboniferous formations outcrop beneath the Permian in the Kharaulakh Range; Lower Cretaceous marine and terrigeonous Tertiary sequences overlie the Permian. Pre-Cambrian, Cambrian, Ordovician, Silurian, Permian, and Triassic strata, and intrusives, little represented in the northwest, outcrop in the southeastern part of the region. On the whole, erosion has not reached the Mesozoic rocks in the northwest.

Tectonically, the Kharaulakh Range consists of folds that have been overturned and thrust to the west. Late Mesozoic tectonic movements have masked the results of Caledonian and Variscan orogenics. The reasons for the arcuate shape of the range are not yet understood.

The quite recent discovery of tin along the Adycha River has attracted geologists to the great basin of the Iana River; geological investigations have not progressed very far, however. The metals are genetically connected

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with Cretaceous granites that have out lower Permian, Upper Triassic, and Jurassic sediments.

Little is known about the Tas-Khaiakhtakh Mountains, with their Cambrian, Ordovician, Silurian, Devonian, upper Paleozoic, Triassic, and Jurassic marine formations; its Tertiary and Quaternary sequences; and its periods of igneous activity (the last igneous rocks were emplaced in Cretaceous times).

The relationships between the Cherski i Mountains and the Tas-Khaiakhtakh are not clear as yet. The former system consists of nine or ten high ranges. Though Paleozoic rocks outcrop at some points, Triassic and Jurassic forma– tions cut by granites dominate the lithology of the mountain system. At some points the Mesozoic sequence also includes Lower and Upper Cretaceous terrigeonous formations. Folds that were thrown up in a Mesozoic synclinorium that formed after the folding of the sediments in Paleozoic times constitute the tectonic structure of the mountain system. These Mesozoic folds are overturned to the north and south. Among the igneous rocks post-Silurian granites and diorites, Upper Jurassic and Lower Cretaceous granites, and Jurassic extrusives are found. Two quite granite intrusions brought in rich deposits of gold and tin.

The Kolyma-Iukagir Platform, northeast of the Cherski i Mountains, served as a central massif around which the Mesozoic geosynclines formed, and against which the folds of the Mesozoic sediments were braced. The Platform itself, however, was subject to fairly strong tectonic deformation. Pre-Cambrian, Cambrian, Ordovician, Silurian, Devonian, and lower Carboniferous formations are encountered; they seem to be geosynclinal deposits and are strongly deformed. In passing from the Cherski i Mountains to the Kolyma-Iukagir Platform, one notices that the Triassic formations lose thickness and turn red. The Jurassic

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sequence includes lavas, tuffs, and coal beds. The Mesozoic formations are folded. Young liparites and teschenites are encountered.

The Kolyma-Okhotsk Divide, which was formerly considered to be a continu– ation of the Stanovoi Mountains, has been found in its eastern portion to consist of terrigeonous upper Permian formations, three divisions of a marine Triassic sequence, Jurassic formations, and a Cretaceous sequence rich in extrusives. Again, in the Okhota, Gusinka, Ulbei, and Kukhtui river valleys, to the west, Triassic-to ^ -^ Cretaceous formations are found ^ to be^ accompanied by extru– sions and granite intrusions. Tertiary sediments and extrusive liparites and marekanites are found along the Okhotsk coast.

The chain of coastal plateaus that includes such ranges as the Sviatoi Nos, the Alazeia, the Polous, and the Aniui is incompletely known. At central points in these plateaus, Cambrian, Ordovician, Silurian, Carboniferous, and Permian formations occur, but Triassic, Jurassic, Lower Cretaceous and, to a lesser extent, Tertiary formations dominate the regional picture. The products of volcanic activity that ended in Quaternary time (chiefly basalts) are widespread. The strike of the folds appears to follow that of the folds of the Kolyma Platform.

Only Bolshoi Liakhovski i Island, in the Novo-Sibirski i Archipelago, has been studied with any considerable thoroughness recently; we must depend upon old data for our knowledge of the rest of the archipelago. A Cambrian sequence is known from Bennett Island, and the Kotelyni Island contains sedimentary formations of Ordovician, Silurian, Devonian, Carboniferous, Triassic, Jurassic, Tertiary, and Quaternary age, as well as Jurassic granites and Tertiary basalts. Tectonically, the island in the southern portion of the archipelago belongs to the Verkhoiansk folded complex. The Paleozoic strata on Bennett Island are

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not disturbed, and this had led some geologists to postulate a Great Arctic Shield which, for the most part, is now submerged.

Recent investigations in this area have brought to light much information on continental glaciations (two or three stages), stream sculpture and pene– planation, permafrost, ground-ice volume, firnification, and soil geology. Several geologists have already written general treatises of the section. Twenty-two investigators have studied the fossil fauna, and four the fossil flora.

Geologists who have participated in the study of the region in spite of handicaps are Atlasov, Vak e ^ a^ r, the Gusevs, Ermolaev, Lazurkin, Nikolaev, S. Obruchev, Saks, Smirnov, Fedortsev, and Kheraskev. Kupletski i made the petrographic analysis of specimens collected by various workers.

The Chukotka-Anadyr section constitutes the eastern third of arctic Siberia. It had been poorly investigated before the Revolution. The discovery of placer-gold deposits in Alaska at the turn of the century occasioned the exploration of the coast of the Bering Sea by the Bogdanovich expedition. R ^ L^ ater the Polevoi expedition penetrated to the central portion of the Anadyr River basin. The investigation of the region made great advances recently; even so, we do not know the geology of the entire area yet. The latest data seem to indicate that the section has three orographic divisions: ( 1 ) the Chukotka Range in its northern portion; ( 2 ) the Anadyr Plateau in its central portion; and ( 3 ) the Gydan and Anadyr ranges (a continuation of the O [] ^k^hotsk–Koly n^m^a Divide) in its southern portion. The Anadyr Depression and its minor mountain ranges, and the Korisk Mountains to the south, are a continuation of the Kamchatka Upland.

In the Chukotka Range there is a belt of pre-Cambrian marbles and crystalline

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rocks that extends from Koliuchinski Bay to the Bering Strait. In addition, geologists have found fossil-bearing Silurian, Devonian, and Carboniferous marine sediments, Permian phyllites, an upper Triassic sequence, and Jurassic coal-bearing and lava-tuff sequences. The pre-Cambrian and Paleozoic rocks strike WNW.-ESE., and are intensely deformed and intruded. The most important tectonic feature of the range, however, is a set of folds of Kimeridgian (Jurassic) date that also strikes WNW.-ESE. Post Jurassic gabbros, mepheline syenite, granites, and acid extrusives enter into the composition of the Dezhnev Range.

The Anadyr Plateaus is made up of Cenozoic lavas and tuffs. Evidence of Quaternary volcanism is present.

The Gydan Range is the divide between the Omolon River (a tributary of the Kolyma) and the Gizhiga. The country rock is pre-Cambrian and Paleozoic. Intruded metamorphic rocks of Proterozoic-Paleozoic age (counterparts of the basement-complex rocks in Alaska) outcrop in these mountains as well as on the coasts of the Bering Strait; in the latter area, however, these rocks are covered by extrusives. The lithology of the Anadyr Range, on the other hand, is dominated by Jurassic, Cretaceous, and Tertiary marine formation, intruded by a variety of acid and alkaline igneous bodies which were emplaced by the various regional cycles of tectonic movement and igneous activity. These injections of magma occurred in Kimeridgian, Austrian, Laramide, and Oligocene time, and later. The same Mesozoic and Cenozoic sedimentary and igneous sequences are found in the minor ranges of the Anadyr Basin.

The Korlak Mountains are, in the main, made up of sandstones, siliceous shales, in part tuffaceous, and great thicknesses of Tertiary sandstone. These sediments were folded in a Tertiary-Quaternary transitional orogeny. Their structure is complicated by normal and reverse faulting, and their strike is NE.-SW. Later tectonic movements have occurred in the area. Coal deposits of Cretaceous and Tertiary age are found at the eastern end of the

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EA-I. Obruchev: Geology in ^ of^ Siberia

mountain system; gabbro, gabbrodiorite, and pyroxenites intrusive are wide– spread in the area, as are porphyritic and a ^ n^ desitic extrusives.

The geology of Wrangel Island was virtually unknown until quite recently. Lately, however, the island was studied in connection with the work of a Soviet Academy expedition which was sent out to collect mammoth remains. The report of this expedition has not been published yet, but it is known that the island is made up of upper Carboniferous and Upper Triassic rocks, the latter of marine origin.

A number of workers have investigated past glaciations of the region, and their effect upon the development of the terrace and permafrost. Data about mineral springs and the peat deposits of the Anadyr tundra has also been gathered. Geologists have collected a few fossil faunas and floras.

Soviet geologists who have gathered most of the information about the section are Artemev, Ditmar, Eliseev, Kudriavtsev, Nikolaevski i , S. Obruchev, Riabkin, and Tikhomirov.

The Kamchatka Peninsula is the only portion of the Asiatic mainland that possesses active volcanoes. It is, therefore, natural that it should have attracted geologists, Russians as well as others, for a considerable number of years. The systematic geological investigation of the peninsula, however, was undertaken only in connection with the post-Revolutionary coal and oil prospecting program, at which time the study of the peninsula’s main volcanoes also became systematic rather than haphazard. Consequently, the main features of the geology of Kamchatka are now thoroughly known.

The Sredinny ^ i^ (Central) Mountain Range constitutes the axis of the peninsula. The outcrops along the crest of the rang consist of gneisses, micaschists, thick phyllites, and Paleozoic argillaceous sandstones. The slopes consist

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of early and middle Mesozoic graywackes and shales (the Volcanic Series), and Tertiary and Quaternary formations. Periodotites, pyro z ^ x^ enites, and some monzonites, outcrop between the sediments. The Paleozoic rocks are intensely deformed; their folds strike almost north-south. The Mesozoic rocks are less deformed and are less deformed and are cut by the necks of extinct Tertiary volcanoes.

East of the longitudinal valley of the Kamchatka River (also under systematic study) stand the peninsula’s eastern coastal mountains. Green tuffaceous shales, the Bogachevka sandstone, four divisions of a Tertiary sequence, dunites, pyro z ^ x^ enites, and young extrusives comprise the dominant rock types.

A broad belt of the western coastal plane is made up of five divisions of a Tertiary sequence, the age of which ranges up to Pliocene. Those sediments contain marine fossils and are covered by Quaternary sediments and basalt flows. These lie upon a surface eroded upon metamorphic Paleozoic rocks in the Sredinnyi Range, and upon Cenomanian and Turonian formations in the Tigil area and at Cape Onman.

At Korf Gulf, in the extreme north, Mesozoic coal-bearing sediments and extrusives are encountered. The coal and petroleum deposits of both coasts have been studied repeatedly.

A great deal of attention has been paid to the study of the peninsula’s volcanoes, particularly Mounts Kliuchevski i and Avacha. Mount Kluichevskii has been under constant systematic study since 1938. Through investigations have also been under constant systematic study since 1938. Thorough investi– gations have also been made of the mineral springs, permafrost, past glaciations, peat bogs, and soils. Paleontologists have studied the dominantly Cenozoic fossil fauna and flora.

The Kamchatka area was a geosyncline up until lower Carboniferous time; then the sediments were thrown into folds which had a NNE.-SSW. strike. These folds were eroded in Cretaceous times and the sea covered them again. The present peninsula is the product of a series of tectonic movements, which occurred between the Cretaceous and Quaternary periods, and which were accompanied by igneous injection and extrusion along fault planes. The earlier Quaternary lavas are basaltic and andesitic-basaltic; the later Quaternary lavas are amphibolites-biotite-andesite.

Among the geologists who have studied the peninsula are Grechish, Dvali, Diakov, Lazarenko, Morozov, Polevoi, and Shcherbakov. Vlodavets, Zavaritski i , Ivanov, Meniailov, and Novograblenov have played leading roles in volcanological studies. Z e ^ a^ varitski i , Krishtofovich, Tebenkov, Kharkhovich, and S ^ h^ cherbekov wrote general geological reports of the area.

In conclusion, we draw attention to the fact that, from time to time, general accounts of the geology ^ ^ of all of Siberia have been compiled from accumulated regional studies, just as general regional studies are based on a synthesis of detailed local studies ^ .^

V. A. Obruchev

	Page
The West Siberian Lowland	4
Northern Kazakhstan	6
The Altai-Saian region	11
The Kuznetsk Alatau and the Shoria Upland	13
The Salair Ridge	14
The Kuznetsk coal basin	15
The Altai	17
The Western Saian	19
The Minusinsk Depression	20
The Siberian Platform	22
The Yenisei Ridge	26
The Taimyr Peninsula	27
The Eastern Saian	28
The Baikal Sh ^ i^ eld, the Aldan shield, the Stanovoi Mountains, and the Eastern Transbaikal	29
The Cisbaikal	30
The Baikal Upland	32
The western Trensbaikal	33
The Aldan Plateau	36
The Stanovoi Mountains	37
The eastern Trensbaikal	38

	Page
The Amur Region and the Southern Maritime Provinces	41
The Amur section	42
The Southern Maritime Provinces	43
Sakhalin Island	45
The Northeastern Region	47
The Verkhoianak-Kolyma section	47
The Chukotka-Anadyr section	51
The Kamchatka Peninsula	53
Bibliography	56

Geology of Siberia: Encyclopedia Arctica Volume 1: Geology and Allied Subjects